zzre: Add line intersections and refactor

[Helco]

For the upcoming actor lighting (also footsteps, some spell fx) we need line intersections. As we commonly have to ignore invisible textures for the visual effects we cannot just use Cast as this only ever returns the nearest intersection. However I will use this opportunity to apply some much needed refactoring in the world of zzre math.

The goal for this PR would be something like:

• Add line intersections
• Move every actual Intersection math into a central IntersectionQueries.cs file
• Move every actual (primitive) Cast math into Ray
• Move every convenience interface methods into IntersectionQueries.Mixin.cs file
• Generalize AtomicSlowCollider and GeometrySlowCollider like was done with TreeCollider
• Add line intersection tests to WorldViewer
• Investigate why Plane and Box are not readonly

I should also rebase the actor commit out of this PR before merging